Abstract

Blue whales produce intense, stereotypic low frequency calls that are particularly well suited for transmission over long distances. Because these calls vary geographically, they can be used to gain insight into subspecies distribution. In the Southwestern Indian Ocean, acoustic data from a triad of calibrated hydrophones maintained by the International Monitoring System provided data on blue whale calls from two subspecies: Antarctic and pygmy blue whales. Using time difference of arrival and least-squares hyperbolic methods, the range and location of calling whales were determined. By using received level of calls and propagation modeling, call source levels of both subspecies were estimated. The average call source level was estimated to at 1 m over the 17–30 Hz band for Antarctic blue whale and at 1 m over the 17–50 Hz band for pygmy blue whale. According to previous estimates, slight variations in the source level could be due to inter-individual differences, inter-subspecies variations and the calculation method. These are the first reported source level estimations for blue whales in the Indian Ocean. Such data are critical to estimate detection ranges of calling blue whales.

This work was supported by the French Ministry of Ecology, the Association DIRAC (France) and the Commissariat à l’Energie Atomique. The IMS hydrophone data have been available through the CEA under CEA Contract No. 169-C-BEFI and CNRS Contract No. 781513. The information released in this paper conforms to the conditions set forth in this contract. The authors wish to thank G. Ruzié, who provided access to the data used in this manuscript, and C. Cotté for helping in data analysis. K. Antier and two anonymous referees provided comments that greatly improved earlier versions of this manuscript. This work represents a portion of F.S.’s Ph.D.